The present invention relates to photodetectors, and, in particular, relates to photodetectors that measure light intensity in a pre-selected range of wavelengths.
Previous photodetectors are of two basic types: semiconductor photodiodes and photomultiplier tubes. Photodiodes have an active material such as germanium, 0.8 to 1.8 microns; indium selenide, 1 to 5.5 microns; and mercury cadmium telluride, 2 to 22 microns. Each compound has a specific range of detection. Typical photomultipliers have a spectral response in the range of 0.3 to 0.8 microns. This range is determined by the photocathode materials and window materials. It is seen from these devices that frequency response is limited by fixed compound characteristics and device limitations such as window materials.
It would be desireable to have a photodetector which is able to detect a wide range of wavelengths by varying mixture ratios, etc.